Particle detectors are known, for example, for detecting particles having a diameter smaller than a preset value. For instance, apparatus are available for measuring particles or particulates PM. Such microscopic particles, which are present in the atmosphere and formed, for example, by dust, smoke, microdrops of aerosol, etc., may present a danger for health and form an environmental risk that affects climate change.
For detecting particles, some apparatus cause an air sample to pass through a channel with a light beam, for example generated by a laser, which, by striking the particles contained in the air, cause scattering thereof. A detector arranged along the path of the scattered light, on the basis of the detected signal, measures the diameter of the particles and counts the number thereof.
For instance, the apparatus “Portable Laser Aerosol Spectrometer and Dust Monitor”, Model No. 1.108/1.109, manufactured by Grimm Aerosol Technik GmbH & Co., KG is a portable apparatus including a mirror that concentrates the light in the detector (see also http://www.wmo-gaw-wcc-aerosol-physics.org/files/OPC-Grimm-model--1.108-and-1.109.pdf).
The above system, which detects the particles in their spontaneous concentration, may, however, be improved as regards to the measurement times, which are rather long. Furthermore, the system is hardly applicable with decreasing concentrations to be detected, requires high laser power, and is cumbersome and costly due to the discrete structure.
Another commercial apparatus “DustMonit”, manufactured by Contec Engineering Srl, includes a controlled constant-capacity pump that draws in the air through a radial-symmetry probe and conveys it into a chamber, where the transported particles are individually hit by a laser beam. The energy reflected by each particle, proportional to its size, is detected via a photodiode and counted (see also http://www.conteng.it/Bollettini/DustMonit_En.pdf).
The above detector has the disadvantage of detecting the particles one by one, and thus has long measuring times. Furthermore, it introduces an error when particles are aligned along the line joining the detector and the source.
It is thus desirable to have an improved detector that increases the detection efficiency, has high sensitivity as well as short measuring times, small dimensions, and low costs.